Associations between matermal cigarette smoking and accelerated placental maturation measured as tissue calcification have been reported. The authors sought to address whether intakes of the dietary antioxidants, vitamin C, alpha-tocopherol, and beta-carotene, were related to placental calcification of the maternal surface and villi in a cohort of smokers and nonsmokers at risk for delivering small-for-gestational age infants. Gross and histologic examination of placentas were used to determine calcification at the surface (n = 1,213) and villus sites (n = 730), respectively, in a prospective study of black and white women who delivered singleton births between December 1985 and October 1988 at the University of Alabama at Birmingham Hospital in Birmingham, Alabama. Controlling for race and gestational age, likelihood of surface and villus calcification increased as smoking levels increased. Significant reductions in villus calcification were related to alpha-tocopherol intake after controlling for smoking and gestation while intakes of beta-carotene and vitamin C were related to significant reductions in calcification for black but not white women. Surface calcification was not found to be related to antioxidant intake. The authors' findings confirm a pathologic relation between smoking and placental calcification and suggest that dietary antioxidants may reduce villus calcification. Am J Epidemiol 1998;147: 127–35.